1. Field of Invention
The present invention relates generally to a method and apparatus for determining nutrient stimulation of biological processes. Such biological processes include bioremediation, biologically enhanced oil recovery, biological leaching of metals, and agricultural bioprocesses such as biological treatment of compost.
2. Background Art
Many biological processes depend upon nutrients to stimulate growth and activity of the microorganisms involved. These nutrients can be organic and/or inorganic materials. Organic materials such as acetate or citrates provide carbon for building new cell material or biomass, and/or energy. Inorganic materials such as nitrates and phosphates provide the nitrogen and phosphorous which are key building blocks for the cells.
An example of the role nutrients play in bioremediation processes Is in the soil vapor extraction processes for remediating ground water contaminated with organic and inorganic materials. The processes described in Billings et al, U.S. Pat. No. 5,221,159 are illustrative. Billings et al, describes methods and processes for in situ removal of contaminants, such as organic and inorganic products, from soil and groundwater by providing one or more injection wells drilled to a depth below the water table and an extraction well drilled to a depth above the water table. Oxygenated gas is injected under pressure through the injection well while vacuum is applied to the extraction well. Most of the contaminants removed from the groundwater and vadose zone are due to biochemical processes. Microbes from the contaminated site are extracted and analyzed to determine the genera present in the samples. Microbes from genera known to be useful in biodegrading the contaminants are then isolated, and the isolated microbes are fermented to increase the numbers of useful organisms. Then the fermented microorganisms are reintroduced through the injection or extraction wells to enhance biodegradation. If necessary, because of low levels of contaminants and consequent low levels of microbes, nutrients are provided to the microbial population to sustain high levels of degradation activity. This method suffers from not knowing, except through trial and error, what nutrient composition should be added for the particular environment involved to enhance the in situ bioremediation that is key to the success of this technology.
A paper presented by the Cullimore et al at the First International Symposium on Microbiology of the Deep Subsurface in Jan. 15-19, 1990, entitled "Development Strategies for the Utilization of In-Well Incubation Devices (IWID) to Establish Management Strategies for the Bioremediation of Chemically Impaired Water Wells and Groundwater Systems" notes the problem of identifying the proper nutrient composition to facilitate the desired microbial activity in bioremediation processes. The solution proposed in this paper is to put a group of test tubes containing different nutrient compositions into the borehole and then adding samples of the contaminated water into the different test tubes. After a one month incubation period the test tubes are removed from the borehole and analyzed.
The Cullimore et al process for determining nutrient addition to stimulate microbial activity suffers from significant problems. First of all the process uses test tubes which measure only the free living (unattached) microbial communities. However, the free living microbial populations are in many systems much less significant than the attached to microbial populations. One study is believed to have shown that biological activity from attached microbial populations was 100 times more significant than that due to free living microbial communities.
Another significant draw-back of the Cullimore et al approach is that the test is essentially a batch culture and thus the test would only represent the chemical conditions of the particular environment at the beginning of the test. Therefore, there are serious concerns about the commercial applicability of the Cullimore et al test.